Nanostructured anion-exchange membrane and method for obtaining same

Abstract

The invention relates to a method for obtaining an anion-exchange membrane which contains an ionomer film, wherein the copolymer chains of the ionomer are arranged throughout the thickness of the film according to a nanostructure having double gyroid morphology, the ionomer being of formula A-B'-C, wherein A is a hydrocarbon polyvinylaromatic block; B' is a polymer block, of which the constituent repeating units each contain a nitrogen-containing aromatic heterocyclic pendant group and in which all or part of the nitrogen-containing aromatic heterocyclic pendant groups are N-alkylated; and C is a hydrophilic polyether block. The nanostructure formed maximises the transport of anions and water through the membrane and improves the operation of a fuel cell or an electrolyser containing such a membrane.

Description

[0001] Nanostructured anion exchange membrane and its production process

[0002] The field of the invention is that of anion exchange polymer membranes intended for use in membrane electrode assemblies for fuel cells or electrolyzers.

[0003] The core of a fuel cell and electrolyzer consists of two electrodes, an anode and a cathode, an electrolytic layer separating the two electrodes, and a catalyst located at the interfaces between the electrolytic layer and each electrode. In fuel cells and electrolyzers, the electrolytic layer is made of an ion-exchange polymer membrane, also called a polymer electrolyte membrane. Ion-exchange membranes fall into two main categories: proton-exchange membranes and anion-exchange membranes. Anion-exchange membranes appear as a promising alternative to proton-exchange membranes because they allow the use of non-noble metals at the electrode-electrolytic layer interfaces and eliminate the need for perfluorinated polymers such as Nafion.

[0004] Among the technical requirements that anion exchange polymer membranes must meet are high ionic conductivity and good membrane hydration. Since the mobility of anions within the membrane from the anode to the cathode is enhanced by the presence of water, good membrane hydration contributes to the proper functioning of the electrochemical device, whether in fuel cell or electrolyzer configuration. Research has therefore focused on the use of block polymer-based membranes that can self-assemble structures with nanometer-scale channels, ultimately ensuring optimal transport of anions and water. Using this approach, CG Arges et al. in the article Chem. Mater.2016, 28, 1377-1389 describe a process for preparing an ionomer film with a lamellar nanostructure derived from the self-assembly of polystyrene-Z> / oc-poly(2-vinylpyridine) (PS-Z>-P2VP) block copolymer chains. The first step of the process described by CG Arges et al. involves annealing the block polymer, which is in film form, to generate a lamellar morphology with preferential lamellar orientation and long-range ordering within the PS-Z>-P2VP film; the second step is an N-alkylation reaction of the pyridine groups with methyl iodide to transform the pyridine groups into pyridinium groups. In order to maintain the preferred orientation of the lamellae throughout the thickness of the film in a direction that intersects the average plane of the film, the thickness of the ionomer film remains limited to a value of approximately 50 nm.Such a thickness proves too small for applications in a fuel cell and in an electrolyzer, particularly in a through-plane ion conductivity configuration. Therefore, there remains a need to provide a process that allows obtaining an anion exchange membrane containing an ionomer film with a thickness on the order of a micron, or even one or more tens of microns, and in which the copolymer chains of the ionomer are arranged (ordered) according to a nanostructure leading to the formation of channels with physical continuity.

[0005] 2024PAT00121WO the entire thickness of the ionomer film to maximize the transport of anions and water into the membrane.

[0006] The inventors have discovered a process for preparing a new membrane that addresses this need.

[0007] Thus, a first object of the invention is a method for preparing an anion exchange membrane containing an ionomer film in which the copolymer chains of the ionomer are arranged throughout the thickness of the film according to a nanostructure of double gyroid morphology, which method comprises the following successive steps: a) Forming a film of a triblock polymer of formula ABC,

[0008] A representing a hydrocarbon polyvinylaromatic block, B representing a polymer block whose constituent repeating units each contain a pendant nitrogenous aromatic heterocyclic group, and C representing a hydrophilic polyether block, b) Expose the polymer film prepared in step a) under a solvent vapor to obtain throughout the thickness of the film an arrangement of the copolymer chains constituting the triblock polymer in a nanostructure of double gyroid morphology, c) N-alkylate all or part of the pendant nitrogenous aromatic heterocyclic groups by contacting an alkyl halide with the polymer film obtained in step b).

[0009] A second object of the invention is an anion exchange membrane containing an ionomer film in which the copolymer chains of the ionomer are arranged throughout the film's thickness in a double-gyroid nanostructure. The ionomer is a triblock polymer of formula A-B'-C, where A represents a hydrocarbon polyvinylaromatic block, B' represents a polymer block whose constituent repeating units each contain a pendant nitrogen-containing aromatic heterocyclic group and in which all or part of the pendant nitrogen-containing aromatic heterocyclic groups are N-alkylated, and C represents a hydrophilic polyether block. The membrane according to the invention can be obtained by the process according to the invention.

[0010] Another object of the invention is a membrane-electrode assembly, AME, for a fuel cell or electrolyzer, which assembly comprises an anion exchange membrane according to the invention, which membrane is capable of being obtained by the process according to the invention.

[0011] The invention also relates to a fuel cell or electrolyzer which includes an anion exchange membrane according to the invention, which membrane is capable of being obtained by the process according to the invention.

[0012] Description of the invention

[0013] The polymers mentioned in the description can be of fossil origin or bio-based. In the latter case, they can be derived, partially or entirely, from biomass or obtained from renewable raw materials derived from biomass. Similarly, they can also come from the recycling of previously used materials; that is, they can be derived, partially or entirely, from a recycling process, or even obtained from raw materials themselves derived from a recycling process.

[0014] The terms "membranes" and "films" are well known to those skilled in the technical field. It is a well-known fact that a membrane is a structure such that

[0015] 2024PAT00121WO as defined by IUPAC, in "IUPAC recommendations 1996"; the term "film" is understood according to the definition given by IUPAC in "IUPAC recommendations 1996". An ionomeric film is understood to be an ionomer that is in the form of a film.

[0016] The term "nanostructure" is well known in the field of polymer science. It is recalled that a nanostructure is a structure in which at least one of the features repeats over distances of the order of nanometers (in English "Structure in which at least one of the features repeats over distances of the order of nanometers", Terminology for aggregation and self-assembly in polymer science (IUPAC Recommendation 2013), Pure Appl. Chem., Vol 85, No 2, pp. 463-492, 2013).

[0017] The block polymer used in step a) of the process according to the invention is essentially characterized by being a triblock polymer of formula ABC. The block represented by the symbol A is a hydrocarbon polyvinylaromatic block. It may be a block of a homopolymer of a hydrocarbon vinylaromatic monomer or a block of a copolymer of several (at least two) hydrocarbon vinylaromatic monomers. In the present invention, a hydrocarbon vinylaromatic monomer is understood to be a monomer of the formula Ar-CH=CH2 or Ar-CR=CH2, the symbol Ar representing an aryl group and the symbol R an alkyl group such as methyl. The aryl represented by the symbol Ar is preferably a phenyl or a phenyl substituted with an alkyl group having 1 to 4 carbon atoms. Examples of useful hydrocarbon vinylaromatic monomers for the purposes of the invention include styrene, styrene substituted by an alkyl group, in para, meta or ortho or alpha positions.The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms. The polyvinylaromatic hydrocarbon block is preferably a polystyrene block. The block represented by the symbol B is characterized by being composed of repeating units, each containing a pendant aromatic nitrogen heterocyclic group. As is well known, an aromatic nitrogen heterocyclic group is an aromatic cyclic group consisting of at least one nitrogen atom. The aromatic nitrogen heterocyclic group is a pendant group of the polymer chain constituting B. The monomer whose monomeric units constitute the block represented by the symbol B is typically a monomer with a double bond bearing an aromatic nitrogen heterocyclic group, in particular an ethylene substituted with an aromatic nitrogen heterocyclic group, for example, a vinylpyridine.B preferentially represents a polyvinylpyridine block, more preferably a poly(2-vinylpyridine) block. The block represented by the symbol C is a hydrophilic polyether. Examples of suitable polyethers for block C include hydrophilic poly(alkylene oxides), particularly polyethylene glycols and polypropylene glycols, and ethylene glycol and propylene glycol copolymers. Preferably, the polyether block is a polyethylene glycol block.

[0018] Preferably, the mass fraction of the block represented by the symbol B in the triblock polymer of formula ABC is greater than 0.20 and less than 0.45, calculated as a mass fraction of the triblock polymer. Also preferably, the mass fraction of the two blocks represented by the respective symbols B and C in the triblock polymer of formula AB-C is greater than 0.3 and less than or equal to 0.45, calculated as a mass fraction of the triblock polymer.

[0019] 2024PAT00121WO The number-average molar mass of the triblock polymer is preferably greater than 12,000 g / mol, and more preferably greater than 20,000 g / mol. Preferably, the number-average molar mass of the triblock polymer is less than 100,000 g / mol. Advantageously, the number-average molar mass of the triblock polymer is more preferably greater than 20,000 g / mol and less than 100,000 g / mol, thus providing the best compromise between the mechanical properties of the film, its filmability, and its nanostructureability. The number-average molar masses are determined by size-exclusion chromatography (SEC) analysis using polystyrene standards.

[0020] The content of nitrogenous aromatic heterocyclic groups in the triblock polymer is preferably greater than or equal to 1.3 mmol per gram of triblock polymer. It is preferably less than or equal to 4.1 mmol per gram of triblock polymer. Advantageously, it is between 1.3 and 4.1 mmol per gram of triblock polymer.

[0021] The triblock polymer with formula ABC can be prepared by sequential anionic polymerization. This involves synthesizing the first block, A, by anionic polymerization of a hydrocarbon vinylaromatic monomer, followed by the second block, B, by subsequent polymerization of the monomer constituting block B, and finally by synthesizing the third block, C, by subsequent polymerization of an oxirane. The triblock polymer can also be prepared by click chemistry, reacting one end of a first polymer with one end of a second polymer. The composition of the first polymer is that of one of the triblock polymer blocks, A or C, and the composition of the second polymer is that of a diblock with formula BC or AB. Alternatively, the triblock polymer can be a commercial product, available, for example, from Polymer Source.

[0022] Those skilled in the art understand that, due to the preparation methods of the triblock polymer, the triblock polymer can be obtained as a mixture containing predominantly by mass, i.e., more than 80% by mass, preferably more than 90% by mass, the triblock polymer, and only marginally the block polymers produced as intermediates in the synthesis of the triblock polymer, such as polymers of formula A and diblock polymers of formula AB. It follows that the polymer film prepared in step a) may contain minor amounts of these intermediates. Typically, the polymer film prepared in step a) contains more than 80% by mass, preferably more than 90% by mass, and more preferably more than 95% by mass of the triblock polymer, with the remainder to 100% consisting of the block polymers produced as intermediates in the synthesis of the triblock polymer.

[0023] The triblock polymer is formed into a film in step a) of the process according to the invention to form a polymer film. The triblock polymer can be formed into a film by depositing a solution containing the triblock polymer onto a substrate surface using techniques known to those skilled in the art, such as the "spin coating," "Doctor Blade," "knife system," or "slot die system" techniques, but any other technique may be used, such as dry deposition, i.e., without prior dissolution. The polymer film prepared in step a) preferably has a thickness of at least 1 µm, and more preferably 10 µm or greater.

[0024] The method according to the invention does not require a specific surface on which is

[0025] 2024PAT00121WO prepared the polymer film in step a). Any surface is suitable provided it is chemically inert to the triblock polymer constituting the film and the polymer film can be in direct contact with said surface. Said surface can be, for example, silicon, Teflon, or glass.

[0026] According to a particular embodiment of the invention, said surface can be pre-coated with a sacrificial layer, and the polymer film is then formed on the sacrificial layer. This particular embodiment can be used to facilitate the subsequent detachment of the polymer film from its support by removing the sacrificial layer, which is triggered at the appropriate time to detach the polymer film from its support.

[0027] Step b) of the process according to the invention typically consists of annealing the polymer film prepared in step a). Step b) promotes a rearrangement of the copolymer chains constituting the triblock polymer by increasing their mobility until a well-defined, double-gyroid nanostructure is achieved. The annealing time is generally on the order of a few hours. Preferably, the annealing takes place over ten hours or more. Solvent vapor annealing is a known method for controlling the morphology of block polymer films. Solvent vapor annealing is characterized by exposing the polymer film to a controlled atmosphere of solvent vapors. A single solvent or a mixture of solvents can be used to perform the annealing.The solvent or solvent mixture, as well as the quantity of solvent, is chosen by a person skilled in the art to swell the triblock polymer without dissolving it. Suitable solvents for annealing include, for example, dichloromethane, chloroform, tetrahydrofuran, 1,4-dioxane, acetone, and mixtures thereof; dichloromethane is advantageously preferred.

[0028] In step b), a nanostructured polymer film is obtained in which the copolymer chains have self-assembled to form a double-gyroid nanostructure, thus creating a three-dimensional network of channels throughout the film's thickness. In other words, the double-gyroid nanostructure is present both on the film's surface and within the film itself, generating channels with physical continuity throughout the film's thickness.

[0029] A double gyroid morphology is known to be a co-continuous three-dimensional structure belonging to the cubic symmetry group Ia-3d and can be identified by surface analysis, atomic force microscopy (AFM), or by indirect grazing angle X-ray scattering (GISAXS) scanning of the film volume. The presence of the double gyroid morphology nanostructure within the triblock polymer can also be demonstrated by direct analysis using scanning electron microscopy (SEM). The coexistence of the three constituent blocks A, B, and C of the triblock polymer makes it possible to prepare a nanostructured polymer film that exhibits a three-dimensional network of channels with physical continuity throughout the film's thickness.

[0030] After annealing, step c) of the process according to the invention is carried out, which is a reaction between an alkyl halide and all or part of the hanging nitrogen-containing aromatic heterocyclic groups of the block represented by the symbol B. Step c) is a reaction modifying the nitrogen-containing aromatic heterocyclic groups into ionic groups containing a quaternary nitrogen atom, by an N-alkylation reaction, the counterion being the halide counterion. The alkyl halide typically has the formula

[0031] 2024PAT00121WO RX, where R is an alkyl group, and X is a halogen atom chosen from iodine, bromine, and chlorine, preferably an iodine or bromine atom. The alkyl group is preferably an alkyl group containing 1 to 10 carbon atoms. Advantageously, the alkyl halide is methyl iodide, CH3I. The amount of alkyl halide and the reaction time are adjusted by those skilled in the art according to the desired content of N-alkylated nitrogen-containing aromatic heterocyclic groups and taking into account the yield of the N-alkylation reaction. Step c) is preferably carried out in a narrow stoichiometric excess of alkyl halide. Preferably, the molar ratio between the number of moles of alkyl halide and the number of moles of nitrogenous aromatic heterocyclic groups is greater than 1, even much greater than 1. More preferably, it is greater than 1 and less than 10.The progress of the N-alkylation reaction can be monitored, for example, by X-ray photoelectron spectroscopy (XPS) by calculating the ratio between the signal areas of the ionic groups after modification and the nitrogen-containing aromatic heterocyclic groups before modification. To carry out this modification of the nitrogen-containing aromatic heterocyclic groups, in step c) the polymer film is preferably exposed to alkyl halide vapors. At the end of step c), the resulting polymer is an ionomer with the formula A-B'-C. The formula A-B'-C differs from the formula ABC by the nature of the central block B', which results from the modification of block B of the triblock polymer of formula ABC by the N-alkylation reaction of all or part of the nitrogen-containing aromatic heterocyclic groups.Since the rearrangement of the copolymer chains obtained at the end of step b) is maintained during step c), an ionomer film that is also a nanostructure is obtained at the end of step c). Indeed, the ionomer film is formed of a three-dimensional network of channels with physical continuity throughout the thickness of the ionomer film. The channels typically have a diameter greater than or equal to one nanometer (nm) and preferably less than 200 nm. The diameter of a channel is defined as the diameter of its cross-section. In the case where the cross-section is not circular, the diameter is the longest dimension of the cross-section.

[0032] The ionomer film preferably has a thickness of at least 1 pm, more preferably greater than or equal to 10 pm. The ionomer film preferably has a thickness of less than 500 pm, more preferably less than 100 pm.

[0033] At the end of step c), the ionomer film is recovered, notably by removing it from the surface used to form the polymer film of the ABC triblock polymer. If a sacrificial layer was used as an interface between this surface and the triblock polymer, it is removed before recovering the ionomer film free from its support. The ionomer film constitutes all or part of an anion exchange membrane for a fuel cell or electrolyzer.

[0034] According to one embodiment of the invention, the polymer film is detached from its support at the end of step b) and before step c).

[0035] According to a particular embodiment of the invention, after step c) a step d) is carried out in which the halide anions are replaced by hydroxide anions. Step d) is typically implemented when using the ionomer film in a membrane during the membrane's water inlet procedure before it is put into operation in a fuel cell or electrolyzer assembly. Water inlet of the membrane is generally part of the break-in or activation operation of the

[0036] 2024PAT00121WO membrane. The operation of replacing halide anions with hydroxide anions is typically an exchange between halide and hydroxide anions and is generally followed by rinsing with deionized water to remove excess hydroxide anions. Rinsing can be performed by immersing the film in a deionized water bath.

[0037] The membrane, another object of the invention, which can be obtained by the process according to the invention, has as its essential characteristic that it is an anion exchange membrane comprising a nanostructured ionomer film, the ionomer acting as the electrolyte. The ionomer film constituting all or part of the membrane according to the invention can be prepared by the sequence of steps a), b), and c) described in the process according to the invention for preparing an anion exchange membrane. The ionomer film has the characteristics of the ionomer film described in any one of the embodiments of the process according to the invention relating to the preparation of an anion exchange membrane containing an ionomer film.Thus, the ionomer film is a polymer film of a triblock of formula A-B'-C, A representing a hydrocarbon polyvinylaromatic block, B' a polymer block whose constituent repeating units each contain a pendant nitrogen-containing aromatic heterocyclic group and in which all or part of the pendant nitrogen-containing aromatic heterocyclic groups are N-alkylated, C a hydrophilic polyether block.

[0038] As is known, an N-alkylated aromatic nitrogen heterocyclic group is a nitrogen-containing aromatic heterocyclic group in which a nitrogen atom is a quaternary nitrogen atom bearing an alkyl group. The alkyl group attached to the quaternary nitrogen atom in nitrogen-containing aromatic heterocyclic groups is preferentially an alkyl group with 1 to 10 carbon atoms, and most preferably a methyl group. N-alkylated aromatic nitrogen-containing pendant groups constitute the ionic groups of the triblock with the formula A-B'-C.

[0039] Preferably, the hydrocarbon polyvinylaromatic block, represented by the symbol A, is a polystyrene block. Preferably, B' represents a polyvinylpyridine polymer block, in which all or some of the pyridine units are N-alkylated. More preferably, B' represents a poly(2-vinylpyridine) block, in which all or some of the pyridine units are N-alkylated. The alkyl group attached to the quaternary nitrogen of the pyridine groups is preferably an alkyl group having 1 to 10 carbon atoms, and more preferably a methyl group. Preferably, the polyether block is a polyethylene glycol block. Preferably, the composition of the ionomer is such that the mass fraction of the block represented by the symbol B' in the triblock polymer of formula A-B'-C is greater than 0.20 and less than 0.45, the mass fraction being calculated relative to the mass of the ionomer.Preferably, the mass fraction of the two blocks represented by the respective symbols B' and C in the triblock polymer of formula A-B'-C is greater than 0.3 and less than or equal to 0.45, mass fraction calculated with respect to the mass of the ionomer.

[0040] The ionomer film constituting the membrane according to the invention is a nanostructured film. It is formed of a three-dimensional network of channels that have physical continuity throughout the thickness of the ionomer film. The channels typically have a diameter greater than or equal to one nanometer (nm) and preferably less than 200 nm. The ionomer film has a thickness preferably at least equal to 1 pm, more preferably

[0041] 2024PAT00121WO greater than or equal to 10 pm. The ionomer film has a thickness preferably less than 500 pm, more preferably less than 100 pm.

[0042] The membrane according to the invention, which contains the nanostructured ionomer film, exhibits good ionic conductivity performance, particularly when used in an electrolyzer. This good performance is attributed to the presence of channels arranged in a three-dimensional network, which have physical continuity throughout the film's thickness and are ionically conductive. The ionic conductivity of the channels is provided by the ionic groups of the B' block. The physical continuity of the ion-rich ion-conducting channels throughout the ionomer film facilitates ion transport within the membrane, thus achieving ionic conductivity values ​​of interest for use in an electrolyzer. The arrangement of the copolymer chains also leads to the sequestration of the hydrophilic C block at the center of the ion-conducting channels.The sequestration of block C promotes excellent ionic conductivity of the membrane through good hydration of block B' located at the periphery of the conduction domains. Furthermore, it ensures better water management within the electrolyte by transferring water from the electrode, where water is generated by electrochemical reaction, to the electrode where water is consumed during the operation of the membrane-electrode assembly. Thus, the nanostructuring that occurs within the ionomer film constituting the membrane according to the invention maximizes the transport of anions and water within the membrane.

[0043] The membrane-electrode assembly (MEA), another object of the invention, is characterized by an anion-exchange membrane according to the invention. MEAs are well-known basic components of fuel cells and electrolyzers. An MEA generally comprises five layers: an electrolytic layer, two catalytic layers, and two gas diffusion layers. The electrolytic layer, which may be a polymer ion-exchange membrane, constitutes the central layer of the MEA; on either side of the electrolytic layer is a catalytic layer; the layer adjacent to the catalytic layer is a gas diffusion layer. The assembly formed by the gas diffusion layers, the catalytic layers, and the electrolytic layer is held together by two bipolar plates. One of the two catalytic layers forms the anode, and the other the cathode.

[0044] The anion exchange membrane according to the invention is constitutive of the electrolytic layer of the AME.

[0045] The fuel cell or electrolyzer, yet another object of the invention, has as its essential characteristic the inclusion of an anion exchange membrane according to the invention. For its use in a fuel cell or electrolyzer, the membrane is preferably activated. As is well known to those skilled in the art, a membrane is primed with water before being put into operation in an assembly constituting a fuel cell or electrolyzer. This primed membrane is generally part of the break-in or activation process. Generally, during this primed membrane process, the counterions of the membrane's constituent ionomer, which are halides, can be replaced by hydroxide anions, which are known to have much better ionic mobility than halide anions. See, for example, the article Energy Environ Sci 2014, 7, 3135.The replacement of halide counterions by hydroxide anions can be implemented by impregnation in the film.

[0046] 2024PAT00121WO of the constituent ionomer of the membrane in an aqueous solution, for example by bringing the ionomer film into contact with an aqueous solution containing hydroxide anions, such as an aqueous solution of a strong base. Suitable strong bases include potassium hydroxide and sodium hydroxide, preferably potassium hydroxide. Preferably, the replacement of the halide counter-ions with hydroxide anions is carried out during the membrane break-in or activation operation.

[0047] In summary, the invention is advantageously implemented according to any one of the following embodiments 1 to 27:

[0048] Mode 1: A process for preparing an anion exchange membrane containing an ionomer film in which the copolymer chains of the ionomer are arranged throughout the thickness of the film in a nanostructure with a double gyroid morphology, which process comprises the following successive steps: a) Forming a film of a triblock polymer of formula ABC,

[0049] A representing a hydrocarbon polyvinylaromatic block, B representing a polymer block whose constitutive repeating units each contain a pendant nitrogenous aromatic heterocyclic group, C representing a hydrophilic polyether block, b) Expose the polymer film prepared in step a) under a solvent vapor to obtain throughout the thickness of the film an arrangement of the copolymer chains constituting the triblock polymer in a nanostructure of double gyroid morphology, c) N-alkylate all or part of the pendant nitrogenous aromatic heterocyclic groups by contacting an alkyl halide with the polymer film obtained in step b).

[0050] Mode 2: Process according to mode 1 in which the hydrocarbon polyvinylaromatic block is a polystyrene block.

[0051] Mode 3: Process according to mode 1 or 2 in which B represents a poly(vinylpyridine) block, preferably poly(2-vinylpyridine).

[0052] Mode 4: A process according to any one of modes 1 to 3 in which the polyether block is a polyethylene glycol block.

[0053] Mode 5: Process according to any one of modes 1 to 4 in which the alkyl of the alkyl halide is an alkyl containing 1 to 10 carbon atoms.

[0054] Mode 6: A process according to any one of modes 1 to 5 in which, in step c) the polymer film is brought into contact with alkyl halide vapors.

[0055] Mode 7: Process according to any one of modes 1 to 6 in which the alkyl halide is methyl iodide.

[0056] Mode 8: A process according to any one of modes 1 to 7 in which: the mass fraction of the block represented by the symbol B in the triblock polymer of formula ABC is greater than 0.20 and less than 0.45, mass fraction calculated with respect to the mass of the triblock polymer, and the mass fraction of the two blocks represented by the respective symbols B and C in the triblock polymer of formula ABC is greater than 0.3 and less than or equal to 0.45, mass fraction calculated with respect to the mass of the triblock polymer.

[0057] 2024PAT00121WO Mode 9: Process according to any one of modes 1 to 8 in which the content of nitrogen-containing aromatic heterocyclic groups in the triblock polymer is greater than or equal to 1.3 mmol per gram of triblock polymer.

[0058] Mode 10: A process according to any one of modes 1 to 9 in which the content of nitrogenous aromatic heterocyclic groups in the triblock polymer is less than or equal to 4.1 mmol per gram of triblock polymer.

[0059] Mode 11: Process according to any one of modes 1 to 10 in which the number-average molar mass of the triblock polymer is greater than 12,000 g / mol.

[0060] Mode 12: Process according to any one of modes 1 to 11 in which the number-average molar mass of the triblock polymer is greater than 20,000 g / mol.

[0061] Mode 13: Process according to any one of modes 1 to 12 in which the number-average molar mass of the triblock polymer is less than 100,000 g / mol.

[0062] Mode 14: A process according to any one of modes 1 to 13 in which the ionomer film has a thickness of at least 1 pm, preferably greater than or equal to 10 pm.

[0063] Mode 15: Process according to any one of modes 1 to 14 in which the ionomer film has a thickness of less than 500 pm.

[0064] Mode 16: Process according to any one of modes 1 to 15 in which the ionomer film has a thickness of less than 100 pm.

[0065] Mode 17: A process according to any one of modes 1 to 16 which includes after step c) a step d) in which halide anions are replaced by hydroxide anions.

[0066] Mode 18: Anion exchange membrane containing an ionomer film in which the copolymer chains of the ionomer are arranged throughout the thickness of the film in a double gyroid morphology nanostructure, the ionomer being a triblock polymer of formula A-B'-C in which A represents a hydrocarbon polyvinylaromatic block, B' represents a polymer block whose constituent repeat units each contain a pendant nitrogen-containing aromatic heterocyclic group and in which all or part of the pendant nitrogen-containing aromatic heterocyclic groups are N-alkylated, C represents a hydrophilic polyether block.

[0067] Mode 19: Anion exchange membrane according to mode 18 in which the ionomer film has a thickness greater than or equal to 1 pm, preferably greater than or equal to 10 pm.

[0068] Mode 20: Anion exchange membrane according to mode 18 or 19 in which the ionomer film has a thickness of less than 500 pm.

[0069] Mode 21: Anion exchange membrane according to any of the modes 18 to 20 in which the ionomer film has a thickness of less than 100 pm.

[0070] Mode 22: Anion exchange membrane according to any one of modes 18 to 21 in which the hydrocarbon polyvinylaromatic block is a polystyrene block.

[0071] 2024PAT00121WO Mode 23: Anion exchange membrane according to any one of modes 18 to 22 in which B' represents a polyvinylpyridine polymer block, preferably poly(2-vinylpyridine), in which all or part of the pyridine motifs are N-alkylated.

[0072] Mode 24: Anion exchange membrane according to any one of modes 18 to 23 in which the poly ether block is a polyethylene glycol block.

[0073] Mode 25: Anion exchange membrane according to any one of modes 18 to 24 in which: the mass fraction of the block represented by the symbol B' in the triblock polymer of formula A-B'-C is greater than 0.20 and less than 0.45, mass fraction calculated with respect to the mass of the ionomer, and the mass fraction of the two blocks represented by the respective symbols B' and C in the triblock polymer of formula A-B'-C is greater than 0.3 and less than or equal to 0.45, mass fraction calculated with respect to the mass of the ionomer.

[0074] Mode 26: Membrane-electrode assembly, MEA, for fuel cell or electrolyzer, which assembly includes an anion exchange membrane defined in any one of modes 18 to 25.

[0075] Mode 27: Fuel cell or electrolyzer which includes an anion exchange membrane defined in any one of modes 18 to 25.

[0076] The aforementioned features of the present invention, as well as others, will be better understood upon reading the following description of several examples of embodiments of the invention, given by way of illustration.

[0077] Examples

[0078] The triblock polymer polystyrene-Z> / oc-poly(2-vinylpyridine)-Z> / oc-poly(ethylene oxide), PS-b-P2VP-b-PEO, (the molar percentage of the PS, P2VP and PEO blocks being respectively 65%, 22% and 13%, Mn 69.5 kg / mol) is purchased from Polymer Source inc. (trade reference P4854-S2VPEO) and used without further purification.

[0079] Preparation of a film Fl according to a process conforming to the invention:

[0080] Step a) (formation of a polymer film):

[0081] A polymer film 25 pm thick is formed by coating the surface of a (3 cm x 3 cm) silicon support, previously covered with a sacrificial layer of poly(3,4- ethylenedioxythiophene) polystyrene sulfonate, with a solution of the triblock polymer PS-b- P2VP-b-PEO, the polymer solution being prepared by dissolving the triblock polymer in a 70:30 by mass mixture of 1,4-dioxane:tetrahydrofuran at a level of 20% by mass.

[0082] Step b) (steam annealed with solvent):

[0083] The film is then exposed to a vapor stream in a 32 sccm / 8 sccm dichloromethane / nitrogen ratio in a chamber maintained at 20°C for 15 h. The stream is obtained by bubbling nitrogen through a dichloromethane bath. The experimental setup used is identical to that described by Gotrik et al., ACS Nano, 2012, 6: 9, 8052-8059.

[0084] Step c) (N-alkylation of pyridine groups, hereinafter referred to as quaternization): The film is then immersed in methyl iodide vapor for 4 h in a hermetically sealed flask containing an open container of 500 pL of methyl iodide.

[0085] 2024PAT00121WO and heated to 25°C. This constitutes step c) of N-alkylation of the pyridine groups, hereinafter referred to as quaternization.

[0086] At the end of step c), the film is detached from its support by dissolving the sacrificial layer in a bath of deionized water.

[0087] Preparation of an F2 film according to a process not in accordance with the invention:

[0088] Film F2 is prepared according to the procedure described for the preparation of Fl, but omitting step b.

[0089] Films Fl and F2 are used to constitute respectively an anion exchange membrane according to the invention and an anion exchange membrane not according to the invention.

[0090] To determine the ionic conductivity of the films Fl and F2, each film, respectively F1 and F2, is then immersed in a 1 M NaOH solution for 1 day at 25°C to carry out step d) which consists of performing the exchange between iodide anions and hydroxide anions, then the film is immersed in a deionized water solution for 30 min to remove excess hydroxide anions.

[0091] Figure 1 is a representation of the equivalent electrical circuit associated with the Nyquist diagram, where W is a Warburg element, L is an inductance, ReElectrode is the ohmic resistance of the electrodes, CAEM is the electrical capacitance of the membrane, and RAEM is the ohmic resistance of the membrane.

[0092] Figure 2 shows a scanning electron microscopy (SEM) image of a cross-section of the polymer film obtained in step a). The electron probe of the microscope is positioned close to the film surface, allowing visualization of the morphology both inside the film near the surface and at the film surface. The lower portion of the image corresponds to the interior of the membrane revealed by the cross-section, and the upper portion, exhibiting periodic patterns, corresponds to the membrane surface. The scale bar represents a distance of 250 nm. A Hitachi S-4800 SEM microscope with an accelerating voltage of 5 kV was used.

[0093] Figure 3 shows topographic images obtained by AFM (AFM Nano-Observer CSInstruments) of the membrane surface state after steps a), b), and c). The scale bar represents 500 nm. Silicon cantilevers (PPH-NCH, Nanosensors) with a typical tip radius of approximately 5 nm were used. The resonant frequency is approximately 235 kHz.

[0094] Figure 4 shows scanning electron microscopy (SEM) images of the cross-section of the film Fl obtained at the end of step c), the images being taken in the thickness of the film: near the top of the film (A); near the middle of the film (B) (at about half the height of the thickness of the film); near the bottom of the film (C); and at the surface of the film that has been in contact with the support (D), the bottom of the film constituting the surface of the film that has been in contact with the support, the top of the film constituting the surface that is opposite the bottom of the film.

[0095] 2024PAT00121WO The scale bar corresponds to 500 nm. A "Hitachi S-4800" SEM microscope with an accelerating voltage of 5 kV is used.

[0096] Ionic conductivity of the Fl and F2 films after the exchange between iodide anions and hydroxide anions:

[0097] Ionic conductivity was measured by electrochemical impedance spectroscopy using a Solartron 1260 instrument over a frequency range of 1 MHz to 1000 Hz with an amplitude of 50 mV. A BioLogic CESH-e cell with 2 cm diameter gold-plated circular electrodes was used. Measurements were performed at 20 °C across the plane after compressing the sample between the electrodes. The ohmic resistance of the membrane was evaluated by parametric fitting of the following equivalent electrical circuit to the experimental results, represented according to the equivalent electrical circuit associated with the Nyquist diagram, as illustrated in Figure 1.

[0098] The ionic conductivity (IC) is then calculated from the well-known formula (1):

[0099] IC= e / (R AE M . S) (1) where e is the thickness of the membrane, RAEM the ohmic resistance of the membrane and S the surface area of ​​the electrodes.

[0100] Results :

[0101] Figure 3 shows that a nanostructure with a double-wave pattern, typical of the double-gyroid morphology, appears during step b) of solvent vapor annealing, and Figure 4 shows that this nanostructure is retained after step c) of quaternization. The images in Figure 4 show that the double-gyroid morphology is present both on the surface and within the film, thus demonstrating that it is present throughout the entire thickness of the film. Comparison of Figure 3 with Figure 2 shows that nanostructuring throughout the entire thickness of the film occurs only if it is carried out in step b).

[0102] After the exchange step between iodide and hydroxide anions in the Fl and F2 films, the ionic conductivity of the Fl film was found to be 1.1 mS / cm, while that of F2 was only 0.2 mS / cm. This significant improvement in ionic conductivity is attributed to the double-gyroid nanostructure present throughout the entire thickness of the Fl film.

[0103] The process according to the invention allows the obtaining of an ionomer film constituting an anion exchange membrane which exhibits a very significantly improved ionic conductivity.

[0104] 2024PAT00121WO

Claims

Demands 1. A process for preparing an anion exchange membrane containing an ionomer film in which the copolymer chains of the ionomer are arranged throughout the thickness of the film in a nanostructure with a double gyroid morphology, which process comprises the following successive steps: a) Forming a film of a triblock polymer of formula ABC, A representing a hydrocarbon polyvinylaromatic block, B representing a polymer block whose constitutive repeating units each contain a pendant nitrogenous aromatic heterocyclic group, C representing a hydrophilic polyether block, b) Expose the polymer film prepared in step a) under a solvent vapor to obtain throughout the thickness of the film an arrangement of the copolymer chains constituting the triblock polymer in a nanostructure of double gyroid morphology, c) N-alkylate all or part of the pendant nitrogenous aromatic heterocyclic groups by contacting an alkyl halide with the polymer film obtained in step b).

2. A process according to claim 1 wherein the hydrocarbon polyvinylaromatic block is a polystyrene block.

3. A method according to claim 1 or 2 wherein B represents a poly(vinylpyridine) block, preferably poly(2-vinylpyridine).

4. A method according to any one of claims 1 to 3 wherein the polyether block is a polyethylene glycol block.

5. A method according to any one of claims 1 to 4 wherein in step c) the polymer film is brought into contact with alkyl halide vapors.

6. A process according to any one of claims 1 to 5 wherein the alkyl halide is methyl iodide.

7. A method according to any one of claims 1 to 6 wherein: the mass fraction of the block represented by the symbol B in the triblock polymer of formula ABC is greater than 0.20 and less than 0.45, mass fraction calculated with respect to the mass of the triblock polymer, and the mass fraction of the two blocks represented by the respective symbols B and C in the triblock polymer of formula ABC is greater than 0.3 and less than or equal to 0.45, mass fraction calculated with respect to the mass of the triblock polymer.

8. A method according to any one of claims 1 to 7 comprising after step c) a step d) in which halide anions are replaced by hydroxide anions.

9. Anion exchange membrane containing an ionomer film in which the copolymer chains of the ionomer are arranged throughout the film's thickness in a double-gyroid nanostructure, the ionomer being a triblock polymer of formula A-B'-C, where A represents a 2024PAT00121WO hydrocarbon poly vinylaromatic block, B' represents a polymer block whose constituent repeating units each contain a pendant nitrogen-containing aromatic heterocyclic group and in which all or part of the pendant nitrogen-containing aromatic heterocyclic groups are N-alkylated, C represents a hydrophilic polyether block, which membrane is capable of being obtained by a process defined in any one of claims 1 to 7.

10. Anion exchange membrane according to claim 9 in which the ionomer film has a thickness greater than or equal to 1 pm, preferably greater than or equal to 10 pm.

11. Anion exchange membrane according to any one of claims 9 to 10 wherein the hydrocarbon polyvinylaromatic block is a polystyrene block.

12. Anion exchange membrane according to any one of claims 9 to 11 wherein B' represents a polyvinylpyridine polymer block, preferably poly(2-vinylpyridine), in which all or part of the pyridine motifs are N-alkylated.

13. Anion exchange membrane according to any one of claims 9 to 12 wherein the polyether block is a polyethylene glycol block.

14. Anion exchange membrane according to any one of claims 9 to 13 wherein: the mass fraction of the block represented by the symbol B' in the triblock polymer of formula A-B'-C is greater than 0.20 and less than 0.45, mass fraction calculated with respect to the mass of the ionomer, and the mass fraction of the two blocks represented by the respective symbols B' and C in the triblock polymer of formula A-B'-C is greater than 0.3 and less than or equal to 0.45, mass fraction calculated with respect to the mass of the ionomer.

15. Membrane-electrode assembly, MEA, for fuel cell or electrolyzer, which assembly comprises an anion exchange membrane defined in any one of claims 9 to 14, which membrane is capable of being obtained by a process defined in any one of claims 1 to 8.

16. Fuel cell or electrolyzer comprising an anion exchange membrane as defined in any one of claims 9 to 14, which membrane is capable of being obtained by a process as defined in any one of claims 1 to 8. 2024PAT00121WO

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